What's your favourite gamification moment in a non-game product?

When we built Wunderlist, the sound when you checked off a task was a fan favourite, and I always loved it. I think the obvious ones are actually in todo list apps as they have a straightforward path to a gamification moment. I do love how we have implemented the moment an article is shown as read and completed and how we track how many articles I have read

levels + unlocking some perks, benefits

I start: the confetti unicorn in Asana that pops up once in a while when you sort a few tasks is pretty fabulous. Not working in Asana at the moment, but I still remember the unicorn...